Understanding the Neural Basis of Working IVIemory to Improve WIVI Function The purpose of this proposal is to conduct basic research to understand the neural correlates of working memory. The second purpose is to then apply our findings to improve working memory function in the healthy aging and in those with traumatic brain injury through novel neurostimulation protocols. First, we will use functional neuroimaging (fMRI) to test two contradictory theoretical viewpoints regarding the role of the posterior parietal cortex in working memory. It is important to understand the role of the posterior parietal cortex to appropriately design therapeutic studies for improving working memory. Thus, the results from the first experiments will guide the design and predicted outcomes ofthe applied experiments in which transcranial direct current stimulation (tDCS) is applied to special populations. TDCS is thought to improve cognitive function through several mechanisms. The tDCS technique involves the application of a safe, low level of electrical current to the scalp. The electrical current passes into the cortex and can transiently increase or decrease the likelihood of neurononal firing in the cortex, and it may also increase the activity in white matter tracts to overcome white matter damage. We predict that anodal (+) tDCS applied to the prefrontal and/or parietal cortices, will improve visuospatial and verbal working memory function by increasing the underactivity of cortical activations in the healthy aging. In a longitudinal study of working memory, we will apply parietal, prefrontal or alternating parietal/prefrontal anodal tDCS to separate groups of healthy aging individuals. The duration of improvement will be tested by bringing participants in for a final behavioral session one month after their final tDCS session. The second set of applied experiments will test whether tDCS can also be used effectively to improve cognitive function in participants with mild or moderate traumatic brain injury. In these participants, there is is often white matter damage. We will conduct experiments to see if alternating parietal/prefrontal tDCS stimulation will improve visuospatial or verbal working memory in those with traumatic brain injury.